The present invention relates to a filter apparatus for removing foreign substances which are contained in foul water to be treated, by passing the foul water through a filter layer which is made up of a particulate filter medium such as sand or the like. The foul water includes river water to be taken in from a river for use as clear water, waste water to be discharged from factories or plants, or the like.
As a conventional filter apparatus, there has been known the following as shown in FIG. 6. Namely, inside a cylindrical container (or tank) d, there is provided a filter layer v which is made up of a filter medium such as sand or the like. In close proximity to a bottom portion of this container d, there is provided a funnel member e whose upper circumferential end is fixed to an inner circumferential surface of the container d. There is further provided a conical sand separator g while keeping a clearance f between a lower end of the funnel member e and the inner circumferential surface of the container d. The clearance f is for the sand to pass through. A raw water intake h is formed between an outer side surface of the funnel member e and the inner circumferential surface of the container d. The raw water to be supplied under pressure into the container d from the raw water intake h is forced upward through the filter layer v to thereby filter the raw water. The filtered water is taken out of the container d through an overflow sluice i which is provided on an upper portion of the container d.
The sand, serving as a filter medium, which has been contaminated or fouled by foreign substances as a result of the process of filtering the raw water is gradually collected, through the clearance f, into a sand collecting box k which is disposed at the lower end of the container d. The collected sand is sent, through a lifting pipe m, together with the raw water which serves as transporting water to a washing and separating device p which is provided at the top of the container d. In this washing and separating device p, fresh washing water is supplied from a supply pipe n which is provided at the top of the washing and separating device p. The sand which is washed by the washing water and separated from the raw water is returned to the container d. After washing the sand, the washing water is discharged from a washing water discharge port r, and the raw water is discharged from a water discharge port s. In this manner, the washing of the fouled filter sand can be continuously performed while the filtration of the raw water is constantly performed.
There is also known one as shown in FIG. 7. In this conventional apparatus, the raw water is supplied circumferentially from a central portion of a cylindrical filter layer v. Water collecting pipes t are disposed in the peripheral portion of the filter layer v to thereby take out the filtered water from the water collecting pipes t. At a bottom portion of the cylindrical filter layer v, there is provided a backwashing water supply port w. An air lift pipe u is also provided through a central portion of the filter layer v. In this arrangement, the filter medium from a highly fouled portion can be washed while it passes through the air lift pipe u.
The above-described conventional apparatuses have the following disadvantages. Namely, in the former apparatus, the washing and separating device p is disposed in an upper portion of the filter layer where the filtered water is collected. Therefore, the raw water which contains therein the filter medium to be discharged out of the washing and separating device p gets mixed with the filtered water. In addition, in this apparatus, the area of the filter layer which comes into contact with the raw water cannot be made larger than the cross-sectional area of the container d. If the area of the filter layer is made larger, the diameter of the container d must be enlarged, resulting in a filter apparatus which is larger in size.
In the latter apparatus, the foreign substances contained in the filter medium are caused to be gradually suspended and separated upward by the backwashing water to be sent upward from the backwashing water supply port w. Therefore, like in the above-described former conventional apparatus, the washing process takes time and the washing cannot be performed sufficiently.
According to one aspect of the present invention, there is provided a filter apparatus for removing foreign substances contained in raw water by passing the raw water through a filter layer made up of a particulate filter medium disposed in a filter tank, the apparatus comprising: a partition wall provided inside the filter tank so as to extend from an upper end of the filter tank downward while leaving a space to a bottom surface of the filter tank such that the filter tank is divided into a supply portion having a raw water supply port and a discharge portion having a backwashed water discharge port; wherein the bottom surface of the filter tank is inclined from the discharge portion downward toward the supply portion, the bottom surface having the filter medium spread thereon in a manner to cover both the supply portion and the discharge portion, the filter medium being filled to such a depth that an upper end of the filter medium reaches at least a bottom end of the partition wall; water collecting means embedded inside the filter medium for collecting filtered water; and backwashing means for backwashing the filter medium.
According to the above arrangement, a stable filter layer which has an angle of repose of the filter medium can be formed on the inclined bottom surface. Therefore, it is possible to form a filter layer of large area of contact with the raw water.
Preferably, the backwashing means comprises: an air lift pipe having a suction port which is embedded into the filter medium in the supply portion and a discharge port which opens above the filter medium in the discharge portion; and a backwashing pipe for supplying backwashing water into the suction port of the air lift pipe. The air lift pipe is provided in at least two in number, one having a suction port which opens into an upper layer of the filter medium and the other having a suction port which opens into a bottom layer of the filter medium. Further, the partition wall is inclined toward the discharge portion at least at a lower section thereof, the lower section having a plurality of openings passing through the partition wall.
According to the above-described arrangement, an upper surface of the filter layer can be set to a level higher than the lower end level of the partition wall. Further, when the backwashing means is operated, the filter medium is sucked from the filter layer into the air lift pipe and is washed inside the air lift pipe by means of the backwashing water. As a result, the backwashing water containing therein the foreign substances is discharged out of the filter apparatus through a backwashed water discharge port, and the filter medium which has been cleaned of the foreign substances is returned to an upper surface of the filter layer in the discharge portion. The filter medium on the bottom surface of the filter tank thus moves toward the suction port of the air lift pipe along the inclined bottom surface of the filter tank. Accordingly, all of the filter medium can be moved into the suction port of the air lift pipe in an orderly manner.
Preferably, the backwashing water to be used in the backwashing means is taken from the water collecting means. According to this arrangement, there is no need of separately providing a tank for storing therein the backwashing water.